This invention relates to a chair height adjustment mechanism and in particular, to a mechanism which can be longitudinally adjusted by rotating an unoccupied seat section.
Rotatable or swivelable chairs developed for office and industrial use have ordinarily been adjustable to vary the height of the seat section relative to the chair base by reaching underneath the seat section and manually rotating an adjustment nut or collar or by withdrawing and reinserting a lock pin or pawl in a seat standard having a series of holes. These means are often unhandy to use and some have even subjected the chair seat to uncontrolled and hazardous collapse. More recent designs utilize a spindle which threadably engages a support column to more positively support the seat section and alleviate substantial possibility of inadvertent retraction or collapse.
Refinement of the spindle and support column arrangement, such as disclosed by Bowman, U.S. Pat. No. 3,870,271 eliminate the inconvenience of having to reach underneath the seat section in order to adjust chair height. In Bowman, a contact arm and lug extending downwardly from an adjusting nut eventually engage a stop extending radially from the hub tube so that rotation of the seat section when unoccupied causes the spindle to rotate relative to the adjusting nut, thereby adjusting the height of the seat section. When the chair is occupied, however, the contact means will not engage the stop and the seat section may be rotated without height adjustment. Unfortunately, this mechanism requires many parts, is complicated and accordingly expensive to construct. Moreover, the contact arm is susceptible to bending or breakage since the chair seat could conceivably be rotated 360 degrees before the contact arm slams against the stop.
Beukema, U.S. Pat. No. 4,324,382 developed a height adjustable chair base also directed to preventing rotation of an adjustment nut when the chair is unoccupied in order to allow height adjustment. The Beukema device requires a spring housing for supporting a support column and aligns the spring and a hub tube to cover an unsightly spindle extending upwardly from the base. The additional expense of the spring housing and hub tube adds substantially to the cost of the chair.